The big freeze: Breakthrough as scientists chill out over frozen semen

Scientists have reported the first successful use of tiny amounts of graphene oxide to protect collected horse semen during the crucial freezing process.

Graphene oxide is a carbon-based material that is used in the production of conductive films and in batteries. It holds considerable promise in the biomedical field.

Researchers say its latest use represents an advance in the cryopreservation of biological materials that are susceptible to damage caused by cooling them to very low temperatures.

Since the discovery of cryopreservation in the 1950s, it has been widely used in medicine, biology and agronomy. However, the inevitable growth of ice crystals during cryopreservation can cause severe ice damage to the material being frozen.

Several products, including glycerol, have been used to limit formation of ice crystals, but some are not totally effective and there are toxicity issues.

Researchers with the Chinese Academy of Sciences, Professor Wang Jianjun, Professor Fang Haiping and Dr Wang Chunlei, turned their attention to antifreeze proteins (AFPs) that protect a broad range of biological organisms that live in subzero environments.

They investigated the mechanism for how these proteins decreased freezing temperature and inhibited ice growth and recrystallization.

The study team, writing in the Angewandte Chemie international edition, described how the ordered arrangement of the water-attracting and repelling molecules on the ice-binding face affected binding to the ice surface and inhibited the growth of ice crystals.

Inspired by antifreeze proteins, they made use of the unique structure of graphene to investigate the effectiveness of graphene oxide in controlling ice formation. Their research showed that graphene oxide inhibited the growth and recrystallization of ice crystals and shaped them into a hexagon.

Molecular dynamics simulation work revealed the formation of stable ice-like water on the surface of the graphene oxide. Thus, graphene formed more hydrogen bonds with ice in comparison with liquid water, which led to the formation of a curve and effectively torpedoed the continuous growth of the ice lattice.

The researchers reported the successful use of graphene oxide as a cryopreservation agent for horse sperm. The graphene oxide showed high ice recrystallization inhibition activity in a culture medium of horse sperm and saline.

Compared with a commercial product, the addition of only 0.01% of graphene into the culture medium of horse sperm, the motility of horse sperm increased from 24.3% to 71.3%.

The study, they said, not only opened a new avenue for the application of materials that are so thin they are considered two-dimensional, but also helped establish a molecular level understanding of antifreeze proteins in controlling ice formation.